Due to the recent increasing incidence of severe weather conditions where high winds with entrained debris have caused widespread catastrophic damage to residential and commercial structures, there has recently been greater awareness that upwardly acting door systems, if strengthened, can prevent or reduce damage to the structures. This can have the effect of greater safety for occupants of the structure, as well as providing an avenue of escape from the structure, if necessary. In recognition, building code officials, insurance company interests and public experience and awareness are dictating the development of door systems with improved wind load characteristics.
One type of reinforcement for sectional doors are termed “active” systems that involve reinforcement that is added to a door system prior to a storm and removed after the storm. Such systems normally take the form of a plurality of relatively substantial vertical reinforcing posts that divide the horizontal span of the door into reinforced areas with increased rigidity. The reinforcing posts are normally placed adjacent the inside surface of a door and transfer forces to the floor and the header above the door. Problems are frequently encountered, particularly in retrofitting these systems, because in many instances garage door headers are not structurally designed to accommodate stresses of the magnitude that may be imparted. Similarly, the bottom of the post must be firmly attached to the floor. If not properly designed the forces at the bottom of the post can result in cracking of the foundation slab or pilings in a dirt floor. Some types of floor anchoring structure protrude above the surface of the floor and may become a potentially dangerous obstruction. Further, these systems have the disadvantage that they cannot be considered an avenue of escape in an emergency, inasmuch as substantial disassembly of the parts is normally necessary to render the door operable for upward movement.
Another type of reinforcement for sectional doors are termed “passive” systems that involve reinforcement that is permanently built into the door section and therefore does not require any installation of reinforcing members or other preparation prior to a storm. A disadvantage of this type of system is that the reinforcing members impart additional sprung weight to the door that requires additional strength in the track system, attachment brackets, counterbalance springs and other components. Moreover, these systems add additional wear and tear on motor operators, or require larger motor operators, because of the inertia of starting and stopping a heavier door. As a result, recent efforts have been directed toward reinforcing structure that adds a maximum windload velocity pressure resistance per pound of additional weight.
Early examples of “passive” systems employed one or more wooden beams extending longitudinally of and attached to each of the panels of a sectional door. Later, steel reinforcing elements similarly positioned and attached were employed in various configurations such as “A”, “Z”, and “J” shaped struts and “C” and “U” shaped channels. However, unless the guide rollers and end stiles to which the reinforcing elements are attached are significantly strengthened, the same early failures tend to occur. Characteristically this manifests itself in the form of distortion or failure of the end stiles often rendering the door inoperative. Thus, the weight of a door may double in order to increase the windload velocity pressure resistance by as little as three to four times.
Another approach to a “passive” system contemplates limiting axial movement of the roller shafts by restraining members thereon, whereby the roller shafts and the panels are tension loaded when the door is in the closed position to prevent buckling of the panels under applied wind loads. The restraining members may be replaced or supplemented with tension rod assemblies. Both the roller shafts and the tension rod assemblies are attached to the hinges that are affixed to the end stiles.